I tried searching for this problem with no luck so here goes. 2001 dodge ram regular cab, auto trans, 5.9cid, 98,000 miles. I had a very leaky radiator, so i finally broke down and bought a new one. Last weekend i swapped out radiators. Everything seemed to go fine but after driving it my heat goes away at idle. driving the truck the air comes out hot but at a stop light the air cools off drastically. as soon as i stop so does the hot air, as soon as i take off the the hot air comes back. The blower motor stays at speed, the air coming out just gets cold at idle. Every time i check fluid level its full. Any help would be greatly appreciated. thank you.

 

Do a search on this subject, I listed some of the things I found, feel the hoses at idle when this is happening, it tells you which direction to go next, if they are both real hot, then it is a flow distribution problem, with the blend door or something else, if one hose is real hot and the other is just a little warm then you could have a huge air bubble in it, , this happens sometimes to my workers when the radiator is replaced or a large amount of water is lost.....

 

Okay after driving the truck on the expressway for 25 miles i popped the hood and felt all the hoses. the two heater hoses where hot, the top radiator hose was hot but the bottom radiator hose was ice cold.

 

did u change your t stat and how cold is it there??

 

No i did not change the thermostat. the temp gauge is in the normal position when warmed up. The outside temp was in the thirties on the weekend and in the single digits Monday and Tuesday. It did not make a difference from the thirties to single digit temps, no heat at idle but good heat driving.

 

Is it possible that a worn serpentine belt or a water pump cause the no heat at idle?

 

I am in the same boat and at wits end. Air trapped in the line is the only thing that can be left to try to remove. My last and final attempt is going to bleed the core by using that funnel that sits on top of the radiator and the prestone flush kit. I am going to pinch off the outlet line and open the cap on the prestone flush kit. That force liquid through the core backwards and hopefully push out any air. I can then cap it off as the liquid flows since the funnell will hold a fair amount of coolant so I don't have to worry about empting out the radiator and being back in the same situation.

 

Before you go through all that... I thought I would let you know I have the same issue. I never sit in my truck and let it idle because of that problem. I just figured the truck is cooling faster than the engine makes heat at idle. The other problem I have is it takes forever to warm up. Even though, I'd rather have my truck run cooler than hotter. You might try blocking off part of the radiator and see what happens.

 

I blocked off part of my radiator with cardboard and it seemed to help, but I got hardcore stuck and had to rip it off as the truck was overheating. Turns out the fan was stopped by snow, which is what was causing it to overheat.

Anyway, moral is cardboard helps.

 

thanks for all the reply's. card board won't work for me. my transmission cooler is in front of my radiator. It just seems strange that my heater worked really good before the radiator change and now it doesn't. When the radiator was leaking the heater would shoot out cold air when the antifreeze got low at idle but after i filled it up it would throw heat at idle again. It does seem to take longer for the temp gauge to move now also.